Conventional ceiling tiles are typically composed of mineral wool and/or perlite in combination with clay filler, paper pulp and starch and frequently a retention aid (flocculant) (e.g., polyacrylamide). These ingredients are made-up into a slurry in water and then filtered, pressed and dried to make a tile. In the manufacture of conventional ceiling tiles, starch is typically added in granular, ungelatinized (“uncooked’) form, in order to be able to retain it in the tile in sufficient quantity for it to act as a binder in the finished tile. In this state it provides no strength to the wet tile, so wood or paper pulp is added in order to give sufficient strength to allow the tile to be pressed and formed in a continuous web. Gelatinization of the starch occurs during the drying process, and the tile develops its full strength during this phase.
Production processes for making mineral wool-containing and mineral wool-free ceiling tiles are known in the art in U.S. Pat. Nos. and 1,769,519 and 5,395,438. In the former, a composition of mineral wool fibers, fillers, colorants and a binder, in particular a starch binder is prepared for molding or casting the body of the tile. The foregoing composition is placed on suitable trays, which are covered with paper or a metallic foil and then the composition is screeded to a desired thickness with a screed bar or roller. A decorative surface may be applied by the screed bar or roller. The trays filled with the mineral wool composition are then placed in an oven for twelve hours or more to dry or cure the composition. The dried sheets are removed from the trays and may be treated on one or both faces to provide smooth surfaces, to obtain the desired thickness and to prevent warping. The sheets are then cut into tiles of a desired size. In the latter patent, mineral wool-free ceiling tiles were prepared using expanded perlite, however maintaining the starch gel binder comprising starch, wood fiber and water which was cooked to actuate the binding properties of the starch gel.
U.S. Pat. Nos. 3,246,063 and 3,307,651 disclose mineral wool acoustical tiles utilizing a starch gel as a binder. The starch gel typically comprises a thick boiling starch composition combined with calcined gypsum (calcium sulfate hemihydrate) which are added to water and cooked at 180° F.-195° F. for several minutes to form the starch gel. Thereafter, the granulated mineral wool is mixed into the starch gel to form the aqueous composition which is used to fill the trays. Ceiling tiles produced in the manner described in these patents suffer from problems in achieving a uniform density, which is an important consideration with regard to structural integrity and strength, as well as thermal and acoustical considerations.
Mineral wool acoustical tiles are very porous which is necessary to provide good sound absorption, as described in U.S. Pat. No. 3,498,404. Methods of manufacturing low density frothed mineral wool acoustical tiles are described in U.S. Pat. No. 5,013,405 which has the disadvantage of requiring a high vacuum dewatering apparatus to collapse the bubbles formed by the frothing agent and stripping the water from the mineral fiber mass.
U.S. Pat. Nos. 5,047,120 and 5,558,710 disclose that mineral fillers, such as expanded perlite, may be incorporated into the composition to improve sound absorbing properties and provide light weight. Acoustical tiles manufactured with expanded perlite typically require a high level of water to form the aqueous slurry and the expanded perlite retains a relatively high level of water within its structure.
U.S. Pat. No. 5,194,206 provides compositions and methods for substituting scrap fiberglass for mineral wool in a composition and process employing a mixture of water, starch, boric acid and fire clay heated to form a gel to which shredded fiberglass is added to form a pulp. The pulp is thereafter formed into slabs and the slabs are dried to form ceiling tiles.
U.S. Pat. No. 5,964,934 teaches a continuous process of making acoustical tiles in a water-felting process which includes the steps of dewatering and drying, the slurry composition comprising water, expanded perlite, cellulosic fiber and, optionally, a secondary binder, which may be starch, and optionally mineral wool, where the perlite has been treated with a silicone compound to reduce its water retention. The components are combined, mixed and a mar is formed and subjected to a vacuum step followed by drying at 350° C. It is noted that starch may also be used as a binder without pre-cooking the starch, because it forms a gel during the process of drying the basemat.
The components of conventional ceiling tiles have the following functions. Mineral wool/perlite provides fire resistance. Clay filler controls density and provides additional fire resistance. Paper or wood pulp binds together the other components while the slurry is wet. Starch is the main binder in a dry tile. The starch is added in granular (uncooked) form to the slurry; thus, the starch does not have any binding properties until it is “cooked” during the drying process.
Ceiling tile manufacturers typically add expanded perlite to ceiling tile formulations to serve as a lightweight aggregate. Adding expanded perlite provides a ceiling tile with air porosity, allowing the tile to have enhanced noise reduction coefficient (NRC) acoustical properties as well as low weight. Depending on the formulation, expanded perlite weight content may range between 10% and 70% by weight of the ceiling tile formulation, or even higher. In certain instances, increasing the weight percentage of expanded perlite may lower the mechanical strength (e.g., the modulus of rupture) of the ceiling tile. This lowering of mechanical strength sets a limitation on the percentage of expanded perlite that may be used in some compositions, based on the targeted mechanical strength properties for the desired ceiling tile.
The present disclosure provides alternate and improved composites for addition to ceiling tiles, flooring products, and other construction products, while maintaining or improving the properties of the final ceiling tile, flooring product or construction product. The improvements are achieved through the addition of microfibrillated cellulose, and optionally one or more organic particulate materials.
The disclosure also describes economical methods of manufacturing such composites. The improved composites comprise microfibrillated cellulose and, optionally, one or more inorganic particulate material. The improved composites may allow the removal of pulp and/or starch from a conventional ceiling tile composition, thereby allowing improvements in the manufacturing process of improved ceiling tiles, flooring products and construction products. Alternatively, the combination of microfibrillated cellulose and starch may result in a synergistic improvement in the binding of constituents of the ceiling tile composition. Such improved products may include high strength, high density and medium density ceiling tiles and wall boards. In some embodiments, the improvements in the process are through elimination of the “cooking” or drying step; at which gelatinization of the starch would normally occur.